The performances of cutting oil used for cutting a target have been conventionally evaluated based on “how much tool wear is suppressed (how long the tool life is)” and “how much the quality of a processed face can be improved (how much a processed face is fairly finished)”. Specifically, the performances of the cutting oil have been evaluated by measuring wear of the cutting tool used in an NC lathe or a machining center, or measuring the surface roughness of the target. Such measurements take a lot of time and effort. Therefore, such measurements are hard to apply to selection and development of the cutting oil.
Three elements for improving processability of the cutting oil are lubricating performance, cooling performance, and welding resistance (Refer to Patent Literature 1, for example). Evaluating each of the three elements readily and accurately is a shortcut to selection and development of the cutting oil. Under present circumstances, the cooling performance is evaluated by placing the heated cutting tool, to which a thermocouple is attached, in the cutting oil and then, checking a temperature curve of the cutting tool.
Similarly, performances of components of various rotating tools other than the cutting tool as well as performances of used oils and cooling water are not independently evaluated readily and accurately. For example, although evaluating the temperature of the welding torch is important for verifying the welding strength and the state of the base material of a clad layer, at present, the temperature of the welding torch and the solvent is evaluated by checking the temperature curve of the base material near a molten pool and other places.